Advanced Television Systems Committee (ATSC) digital TV (DTV) transmission scheme can transmit high quality of image at a high data rate, but is greatly dependent on multipath signals with large amplitude or characteristics of Doppler shift. Therefore, in poor channel environments, such as indoor reception environment or mobile reception environment, an equalizer of a DTV receiver does not completely compensate for channel distortion, thus greatly degrading reception performance. To solve this limitation, channel distortion that must be compensated by the equalizer is reduced by performing signal processing in spatial domain as well as time domain.
Conventional beamforming techniques that can achieve a spatial signal processing are classified into an adaptive beamforming signal processing and a selective beamforming signal processing.
The adaptive beamforming method calculates beamforming weight coefficients in real time and adaptively. On the contrary, the selective beamforming method forms several beams using weight coefficients fixed in a designated direction and selects a signal having the highest reception performance among several beam outputs. Consequently, the selective beamforming method can be implemented more easily than the adaptive beamforming method and has a high applicability to the DTV system.
That is, the selective beamforming method draws attraction because it can improve the reception performance in a relatively simple way by the combination with the DTV receiver. Regarding a received signal passing through the selective beamforming system, multipath signals are somewhat removed and then inputted to the DTV receiver. Therefore, the equalizer of the DTV receiver can compensate for the distorted channels in a relatively simple way.
However, since the conventional selective beamforming method also selects only one of several beam output signals, there exists the limitation in improving the reception performance. Therefore, there is a demand for calculating beams with channel characteristic improved much more than the selective beamforming method by selecting more than two beams satisfying a criteria condition of channel characteristic, instead of selecting only one beam output signal, and combining selected beam output signals.